Flight position and force indicating



A. Z. BENDAR *GHT POSITION AND FORCE INDICA TING INSTRUMENT 5Sheets-Sheet l Filed May 24, 1941 Sept. 14, 1948.

A z. BENDAR FLIGHT POSITION AND FORCE INDIGATING INSTRUMENT 3Sheets-Sheet 2 Original Filed May 24, 1941 INVENTOR. I Harm/2'2. BEA0.42.

mama/M Sept. 14, 1948. z, BENDAR Re. 23,038

FLIGHT POSITION AND FORCE INDICATING INSTRUMENT Original Filed May 24,1941 3 Sheets-Sheet 3 INVENTOR 4 7/102 2. Bax 042 BY 04mm 7W Reissue dSept. 14, 1948 FLIGHT POSITION AND FORCE INDICATING INSTRUMENT Arthur Z.Bendar, Burbank, Calif.

Original No. 2,320,505, dated June 1, 1943, Serial No. 394,967, May 24,1941. Application for reissue November 18, 1944, Serial No. 564,076

26 Claims.

This invention relates to a flight position and force indicatinginstrument for aircraft.

The primary object of this invention is to provide an instrument forindicating the position of an aircraft in flight and for indicating theforces acting upon the craft incident to a change in direction offlight, a spin, acrobatics, etc.

A further object is to provide a device of this character utilizingliquids for indication of flight position and force, wherein two liquidsof different specific gravities are employed in a manner to affordcomplete compensation for expan sion and contraction, and to modulatethe action of the instrument in all indicating conditions and positionsthereof.

A further object is to provide a device of this character which gives aclear indication of the nature of any variation of the position of acraft from normal flight position, and of the correction or adjustmentof the controls of the craft necessary to restore the craft to normalflight position.

A further object is to provide a device of this character which willindicate the following flight conditions: nose high and nose lowpositions, inclined wing positions, improper turns, relation of appliedstresses to the maximum stress limit of the craft, rate of climb, andsudden updrafts.

A further object is to provide a device of this character which willindicate the forces exerted upon a craft in making right and left turns,in pulling out of a dive, in rapid climbs incident to sudden updrafts,and incident to various manipulations and maneuverings of a craft inacrobatic or stunt flying.

A further object is to provide a device of this character which isnovel, simple and inexpensive in construction, which is easy to install,and which is self-contained.

A further object is to provide a device of this character having aliquid chamber containing two liquids, each of a given anddistinguishing color, and of different specific gravities, together witha liquid displacement member of a specific gravity lower than that of atleast the heaviest of the two liquids, wherein said displacement memberis mounted for movement transverse of the plane or level of separationbetween the two liquids.

A further object is to provide a device of this character having aliquid containin chamber provided with a transparent portion andcontaining quantities of two liquids of different speciflc gravities andof contrasting colors, wherein said transparent member carries markingsof the same color as said liquids and positioned adjacent the plane ofseparation of said liquids, whereby the markings are normally invisible,but are subject to exposure against the background of the liquid ofcontrasting color upon a change in the position of the chamber and itstransparent portion.

A further object is to provide a device having a liquid containingchamber receiving a buoyant liquid displacement sphere, and meansmounting said sphere to modulate the action thereof incident to theapplication of centrifugal force to the device.

A further object is to provide a device of this character having aliquid containing chamber receiving a buoyant liquid displacementsphere, a weight yieldably connected with said sphere, and yieldablemeans normally counterbalancing said weight.

A further object is to provide a device utilizin the level of a liquidfor indication of the flight position of an aircraft, and provided withmeans correcting for temperature variations to which the device may besubject in flight.

Other objects will be apparent from the description, drawings, andappended claims.

In the drawings:

Figure 1 is a face view of the instrument.

Figure 2 is a view of the instrument in side elevation.

Figure 3 is a longitudinal vertical sectionalview taken on line 3-3 ofFigure 1.

Figure 4 is a face view of the crystal of th instrument.

Figure 5 is a side view of the crystal of the instrument with partsshown in section. v

Figure 6 is a side view of the instrument wit parts shown in section toillustrate the positions of the liquids when the instrument isindicating the application of force to the craft.

Figure 7 is a longitudinal vertical sectional view of the frame of theinstrument taken on line 3-3 of Figure 1. t

Figure 8 is a transverse vertical sectional view of the instrument takenon line 8-8 of Figure 7.

Figure 9 is an end view of the rubber sealing sleeve of the instrument.

Figure 10 is a longitudinal sectional view of the sleeve taken on lineIlll0 of Figure 9.

Figures 11 to 22, inclusive, are diagrammatic views of the instrumentillustratin the various indications which may .be obtained therefromasthe same appear to the pilot of a craft when the "portion of -t'he' boreo'f frame :part 23.

ing member has a tubular portion 36 projecting forwardly 'fromskirt 35into the concavity of the 3 instrument is mounted upon the instrumentpanel of the craft.

Figure 23 is a diagrammatic view of the path of flight of an aircraftillustrating a dive and recovery.

Referring to the drawings, which illustrate the preferred embodiment ofthe invention, thenu-; meral designates the frame of the instrumentwhich is preferably formed of metal and may constitute a die casting.Frame 20 comp-rises groove 45 in the inner face of ;a cllosure plate 46screw threaded in the enlarged outer end of 1 the bore of portion 24 andpressing against a a substantially semi-spherical concave-convex portion2| whose concave face is substantially semi-spherical. Portion 2| has 1an annular flange 22 adjacent its outer edge. A generally cylindricalframe part 23 projects'from the 'cen ter of portion 2| with its axispreferably perpendicular to the plane of the outer edge of thesemi-spherical portion 2|, and has a bore extending longitudinallytherethrough. A generally cylindrical portion 24 projects downwardlyfrom portion 2 3, and its "axis is perpendicular to the axis ofportion'23. Portion 24 has an apergture'd longitudinal borecommunicating with the bore of portion 23. The semi-spherical frameportion 2| has an enlargement 25 receiving a screw '26 whose head seatsupon a sealing gasket 21. ,The aperture in portion 25 constitutes aliquid filling opening for the device.

The bore of cylindrical portion 23 communicates with the concavity ofthe portion 2| and is o'fjrestricted tapered form adjacent its inner endto provide an annular shoulder 28 for purposes to be hereinafterdescribed. The outer end of the bore of cylindrical frame part 23 is ofenlarged step formation to receive a split bearing {29 "providing auniversal joint mounting for a sphere 30, and to receive an annularscrewthreaded retaining nut 3I pressing against a sealing gasket 32 andagainst the outer bearing 29. A tubular member 33 fitssnugly within theof "the cylindrical portion '23 and is tapered at 34 substantiallycomplementary-to-the taper "of the bore of frame part 23. A flexiblemember preferably formed from oil resistant, flex- "lble, sealingmaterial, in the nature of artificial rubber, such-as neoprene or thelike, has an annular skirt portion 35 clamped-between the taperedportion 34 of sleeve 33'and the tapered The sealsphericalframe portion2-1, and terminates in a small diameter collar portionn3'l. sAnelongated rod 38, of a diameter much smaller than the inner diameters-of tube 33, and sealing sleeve portion 36, is varied by sphere 3D andextends ;longitudinally .and freelythrough the tube 33 and'the-sealingtube 35, 36, 31 and projects for- -wardly beyond the plane of theouteredge of the semi-spherical frame portion 2!. The collar mortion 31of the sealing tube is of a size to fit and the aperture 39 forconnection at its upper' end with the rod '38. At its, lower end, coilspring 4-! mounts a weight 42 whose diameter is less than the-diameterof the bore of 'thepo'rnon-.24 for the major portion of its length, nwhich has an enlarged diameter portion 43 adsuitable annular gasket 41for sealing the parts. In diametrically opposed relation to opening 39'the tube 33 is provided with an aperture 48 which communicates with anenlarged screw threaded bore 49 in frame portion 23. The open end of anelongated hollow or chambered member 40, whi'eh is closed at its outerend is threaded in bore 49. Member 50 includes an enlarged hexagonal nutportion 5| which seats against an annular sealing gasket 52.

A substantiall semi-spherical concave-convex, transparent crystal orglass 53 has its edges bearing against annular gasket 54 atfthe-outeredge offra'me portion 2|. Crystal 53 is 'held in place by a bezel ring55 fitting therearound and also around the front end portion of thesemispherical frame portion 2|. Bezel 55 terminates adjacent the annularflange 22 of frame 2ll and is secured theretoby screws 56 passingthrough flange 22 and into a rear edge of the beze1 55. The interiorradius of the crystal 53 is the same as the interior radius of thesemi-spherical frame portion 21. Thus, when said parts areinterconnected by bezel 55, a substantiall spherical cavity 51 isprovided which has a fluid tight seal at the junction of the parts byvirtue of the compressed annular gasket 54 between the parts. The bezelis preferably provided with an enlarged mounting flange 58 adjacent itsouter end from which :project' ears 59 'apertured atfill to receivesecuring means for attachment of "the instrument to'an instrument panel.

vWithin the spherical cavity 51 of the instrument is positioned a sphere6i of-a radius slightly smaller than the radius of thespherical'cihamher, 51. Thus, if the spherical chamber 51 is 52 inchesin diameter, sphere 6| will preferably be approximately 2 inches indiameter. here shown, sphere '5! is'solid and isradially recessed ati52for'the free reception of thesealing tube'36-31 It will be understood,h'oweven'that "sphere'fi'l maybe hollow if preferred or neces- "sary.Sphere 61 is provided with a radial *bore coaxial with recess 62 inwhich the elongated rod 38 fits snugly. Sphere BI is provided-withanother bore substantially perpendicular to the bore receiving rod 38 inwhich ismounted an elongated retainer "rod '33 having apointed end "34fitting in "a recess in the rod 38 and having enlarged screw threadedportion '65 for holding the retainer 63is place. The space between thewalls of sp'herical'chamber' 5'! and sphere 6| is filled with .aquantity'of mercury 66 or other liquid havinga high specific gravity-anda disftin'guishingycolorjand a quantity "of a viscous liquidfil, such asdark colored oil, havinga specific gravity substantiall less thanand ofa color contrasting to'that of the mercury or'oth'er liquid 55.These'twoliquids preferably-completely fill the space between the sphere6| and the walls of spherical"chamber 51. The sphere fil is formed ofanyma'ter'ial, such as Cel1uloid,'wood, synthetic resin, or the like,which has A a specific gravity less than the specific gravity of themercury or other =1iquid' 56, and also preferably although "not"essentially less than the 'specific chamber 51.

amount of the two liquids.

gravity of the oil 61. Hence, the sphere GI will and oil 61 which areemployed are preferably such that when the sphere BI is inthis normaleccentric position, the plane 68 of separation between the liquids 66and 61 will coincide with the horizontal center plane of the sphericalIn view of the proportions of the parts set out above as illustrative,the liquid 66 will comprise approximately 75% of the total Iti-s notedthat if desired the contrasting color between the liquids could beobtained by using a clear oil and properly coloring the outer surface ofthe displacement member.

The crystal 53 has suitably applied thereto preferably at its concave orinner face, a linear marking 69 extending thereacross with its upperedge coinciding with the plane of separation of the liquids 66 and 61.Marking B9 is of the same color as the mercury or other liquid 66, sothat it blends with the mercury and cannot be discerned from the mercurywhen the instrument is in its normal positionv Crystal 53 is providedwith a second linear mark 10 extending thereacross and longitudinallyengaging the mark 69. Mark I'D is of the same color as the oil or otherliquid 81 whereby it cannot be discerned from said oil when theinstrument is in normal position. Adjacent and below the opposite endsof the mark 69 are applied a pair of oppositely outwardly pointingarrow-shaped marks H of the same color as the mercury. At the center ofthe crystal is formed a downwardly pointing arrow 12 projecting fromline 69' and also of the same color as the mercury. In ad jacentparallel relation to and above the opposite ends of the line H! areapplied opposite inwardly pointing arrows 13 of I the same color as theoil 61, and at the center of the crystal and projecting above the line10 is formed an upwardly pointing arrow-shaped mark 14 of the same coloras the oil. be applied to the crystal 53 above the line Ill a pluralityof spaced horizontal marks or lines 15 of the same color as the oil andadjacent the arrow 14, for purposes to be hereinafter set forth.

The forward edge 16 of the bezel 55 is preferably provided with a pairof horizontally opposed indicia pointers 11 positioned to coincide withthe normal plane 68 of separation of the liquids 66 and 61. Bezel face15 is also provided with a plurality of angle indicating lines 18 andnumerals 19 displaced and 60 degrees from the indicia 11.

Referring to Figure 3, which illustrates the normal position of theparts of the device, it will be observed that the sphere 6|, by reasonof its buoyancy is normally positioned at the top of the sphericalchamber 51. Rod 38 extends at an angle relative to the horizontal, buthas a clear ance with the tube 33 through which it passes. The rubbersleeve 3536-31 seals the liquid containing spherical chamber 51 from thetube 33, and by virtue of its flexibility, accommodates the angularposition of the rod 38 and variations of said position, without applyingany restraining-stress upon said rod or upon the sphere 6|.

The amount of mercury 66 employed in the device is just adequate toextend to the horizontal center plane of the spherical chamber 51 whenthe sphere BI is in said upwardly offset position, and a much smallerquantity of the Also, if desired, there may or representative ofthe'applied force.

oil or'other liquid 61 is required to fill the re mainder of the spacein the spherical chamber.

When the sphere 6| is moved toward the central and lower portion of thechamber, said sphere displaces the mercury 66 and raises the plane 68 ofseparation between the liquids 66 and 61', as is best illustrated inFigures 6, 14, 15 and 16. Thus, the instrument will indicate by 'meansof the raised level of the plane of separation B8 of the liquids, withrelation to the lines 15 upon the crystal 53, the amount of travelor-movement of the sphere BI and as will be hereinafter explained thismovement is effected by and isin proportion to the amount of force towhich the craft is being subjected. Since the travel or movement of thesphere BI in the spherical chamber will be proportional to the amount ofcentrifugal force applied, the marks or lines 15 may be calibrated todesignate the amount of force or stress to which the craft is subjected.

In the operation of the instrument, with the aircraft in normal flightthe parts will be in the position shown in Figure 3, the sphere 6| beingat the upper portion of the chamber and the indication being as shown inFigure 11 with the plane 58 of separation between the liquids at thehorizontal center of the crystal 53. The weight 42 is fullycounterbalanced by the coil spring 44 and so long as the craft is notsubjected to any force or stress, said weight will remain in its upperor raised position. The weight is of course connected to the rod 38 ofthe sphere by the coil spring 4i so that any downward movement of saidweight is transmitted to the sphere.

When the aircraft is subjected to any stress having a componentoi'centrifugal force, as along the portions a, b, c, of the path offlight illustrated in Figure 23, that centrifugal force acts upon theweight 42. It will be understood that centrifugal force tends'tomultiply the effective weight of all. partsof the device including theweight 42 and since the compressive and expansive forcesof thecounterbalancing spring 44 and connecting spring 4| remain constant, itwill be obvious that the centrifugal force acting upon the weight willcause downward movement thereof within its cylinder.- The amount of thismovement 'Will be in direct proportion to the amount of centrifugalforce applied and therefore the travel or movement of said weight 42 isindicative Since the weight is connected to the sphere 6| through thecoil spring 4| and rod 38, it will be apparent that the movement ortravel of the weight 42 is transmitted to the sphere to displace saidsphere downwardly into the liquid within the chamber, whereby the plane58 of separation between the liquids is caused to rise with respect tothe horizontal center of the crystal 53. Because the movement of thesphere is in accordance with the amount of movement of the weight 42 andthe latter is proportional to the applied centrifugal force, said sphereis moved in accordance with such applied force and the rise in the plane68 of separation between the liquids 66 and 61 in the chamber provides adirect reading or indication of the amount of force or stress to whichthe aircraft is sub- J'ected.

It is noted that the weight 42 is normally counterbalanced by the spring44 so that said weight is normally held in suspension and is therebysensitive toanyslight force applied thereto. The mass of the weight 42is greater in proportion to the mass or weight of the sphere GI and byproexnausi n o he par t aeei s a hevhaelierpundiQf viding the; coilspring connection; 4.1 betweensaid weieht a d. th a 'said' s ing l teh so ov come, and compensate for. .the inentia. action Mith r ElEhi 42 a tccommodatea modulated and somewhat delayed; action of, the; sphere-6|which necessarily occursby-reason of. the noose sity of; moving thesphere ,5! within the liquids '66 andBI. -'I herefore, the combinationand arrangernent of the pants, and particularly of the springs 4;]; and44, is such thatv the responseof deyice-prevents over travelv 0f;the-sphere 6| apdgprovides aquick returnof the, parts tonormal positionas illustrated in-EigureB assoon as. the cm. ea o c s b enrehe mThe-provision; of.- the flexible sealing; sleeve. with portion 36thereof spaced from therod 38 accommodates for variations in-pressure.-and tempera..- ture, tending to vary the volume, of the liquids be or.61. Thus, for example; in the event: oi a temp r t re is w ich wil in rase th volum of the liquid, and particularly the'volume of the mercury,the expanded. liquidwill pressinwardly against the;sleev.e-.3 6 tocause'the same tocollapse o le ward an ra i l y and thus: commodate forthe increased volume of the liquid. without destroying the value ofthegsleeve as a seal or itsflexibility. In the event of adecrease inempe re, he on y re t will e t lower, h liquid-level 6 8 which willserve toindicate to the pilotthe temperature'drop and hence permitvh mto; make the necessary mental-corrections of the instrument readings.Any changein the air pressure wi-l1;haveno substantial. effect .upon theinstrumentbeca-use of its sealed connection.

A. l quid-- ma e. provid n; he i terior of. tube liv n inthe bo of. h usnernort om toteiv adash p t actionunonzmav meht-Qf. the w i ht- Such liqid w lse-xte idz ans ax matelr he level of the base ofthe fitting .59, so thatan air pocket is .prov dedwi h nthe fi tin 5.0 tauompens teio'quid;o henees;hi airnr ssur One; t ar 'pu no estoi. the. ns rument is od a e thfi'position q heaira aft fli ht;

that; to. ind cate; any. variation: he; po itio or the raft rom: n rmal.r level a fli h positi n. wi litre n tb th. the ter l. andtth s lonitudin li es of. he aft Th -Ope ation of; he d vice o d a va i us;nditions of. the craf flight have been, illus rated. n u e '11 to 32;nclusi e. wh chwill e eierreditolspe ificail for the purp o explaininthe, p ion: of

the. inst um n and: he in ication btained -there from E eur l r t th insument .3 same ap r n no m l. fl ht. N te thattonly the lineof se a ationofv the tw c ntrast ng,- liquids itil i v sible,.an h hisi in t ndsbetwe 13.12 5 indicia. 1:1 on. the bezel, -15.- Q f. he-d vice: o desina e a l e i h ndit on- Fi ure 2.-illustrates. a .fliehtu ondiionimthethe lei-t wi s w ed so. that theransve se. a is o :the-plane is.30. de rees-disp aced romnormal Wh th di ec ion; 33 fli ht; s. su stan aly straight! viii; is, inc-l ned. with respec In thi cend ti heiiiquisi1e 1;

he tr nsa ted as the nstrument s;viewed.bys herailotrand point o. he:meral 3.;- o; desisna etaz MYQQEE-Q an l Qf: nc ina ion- Th Sj; tilting;Q the instrunient relative to the horizontal exposes the rightend of.mar Bil-and the. eft d-: at ne. 1.1L a ainst the ack r und of h1.=1-iquisi -ll nd fialEfiRQQ- tivel A so, the. left: ar ow tfi ecomes:n-

and; the mercu y colored a e D.-

par nt esains hezbe kemund. t-th woilltl. lil

:8 virtuei h arra gem of the tr wsr'll -and 1.3 the, two arrowswhichare-exposed, in the. con,- dition. .of. flight illustrated. in.1iigure.12 pointin thesamedirectmn; -namely,..t0 the right, toindircatethgdirectioninwhich the control stick, of zthelcraftshould'be moved for.the purpose. of, re.-

? ing color; hence 15PM desi nates the angle of inclination and-thearrows pointtoth lefttoindicate that a movement of the stick .t o,the.le ft isrequiredytorestore the craft to normalflight.

Figure 1.4-, designates the appearance of: the instrument when.- thesameis indicating. atoms or stress. condition. only, as. when the aircraftis entering or pulling out of a dive.- Note-that the liquid. level 68has been raised. When.,level is read with respect to the calibratedindicia l5, it-indicatesthe amount: of the force onstress to:whichthecraft is being subjected. Also, it will. be noted. that theline [0 and the. arrows I3 ofthe color of the oil 6'! become apparentagainst the background of themercury 66,. as does also the arrow 14.Hence, when the instrument. appears as illustrated in. Figure 14, thepilot is informed of the fact that hisship is out of longitudinalbalance and is being subjected to centrifugal or other force .or-stress.

The exposure of the arrow 14 indicates to. the

pilot that it. is necessary for him toeloring the shipinto longitudinalbalance, whilethe parallel Figure 15 illustrates the-reading ofv theinstnument when theleft wing of the plane is low. and the plane is beingsubjected to stress. Note that the level. .ofthe'plane 68 has beenraised toexposeqth-e lines Mk-and thearrows l3 and 14,.and that saidplane 68 is substantially parallel tothe line 10. so thatthe reading isthe same as in Figure 14, namely, one. which indicates force only, if:the craft is banked the amount. re-

quired for the turnnwhich occasions the centrifugal force. Whenthe stickis. pushed,,forward, as indicated by the arrow 14, the instrument willgive, areading similartoFigur-e 12. The same- .condition exists when theright Wing is low, as illustrated in Figure 16. Thus, though theinstrument indicates both theflight position and the. applicationof-force-thereto, the readings are not obtained simultaneously inmost-instances, since. the force indication may blank. out the position.indication initially, so that: the position indication. isobtained onlyafte1''the forcev applying condition. is corrected. It may alsoY bementioned that. during a loopor arol-l, the-positime of the; two liquidswill continually change inasingle-i direction, as will be; obvious andobservanceofthe movement and its direction will indicate theinat-ureofthe maneuver tothe pilot.

Eigure L7 illustrates the indication given by theiinstrument when; theaircraft is in astraight climb ornose high position. The line 68 ofseparationbetweemthe liquids hasbecome. curved in formand-extendsbetween. indicia ll of; the bezel 6 :1; to exposesubstanti-ally the: full. length of line In; the inner-portions ofarrows 13; and

at least a portion of arrow 14,. all. of which are all ;the same coloras; the oilifl and appear 9 against thecontrasting background of themermay 66. This informs the pilot that he must push forward on the stickto return the craft to longitudinal balance.

Figure 18 indicates a condition wherein the plane is in a climb with theleft wing low. The liquid level line 58 is curved and points to thenumber 3 at the left to give a reading of the extent of lateralinclination of the craft. The left part of line Ill and the right partof line 68 are exposed, together with the left arrow 13 and the rightarrow H, which indicate that amovement of the stick to the right, inaddition to a forward movement thereof, is required to restore the planeto normal iiight.

Figure 19 indicates the reading given by the instrument when the craftis in a climb or nose high position with its right Wing low.

Figure 20 illustrates the appearance of the instrument when the craftis'in a dive or nose low position, with the lateral axis of the plane instable or horizontal position. The mercury colored line 69 is exposed byvirtue of the downwardly curved form of the line 68 of separation.between the liquids. The mercury colored arrows H and 12 are alsoexposed against the background of the dark colored oil 61. When thisreading of the instrument is observed, the pilot is informed therebythat it is necessary for him to pull backwardly on the stick in order torestore the plane to normal flight.

Figure 21 illustrates the appearance of the instrument when the plane isin diving or nose low position with its left wing low. The line 68 ofseparation of the liquids curves downward- 1y with its left end high andpointing to the indication upon the bezel'lfi which constitutes ameasurement of the degree of lateral displacement. At the same time, theright end portion of line 69 and the left end portion of line H! areexposed, together with the left arrow 13, the right arrow H, and thearrow 12. This reading of the instrument informs the pilot that it isnecessary for him to move the stick backwardly and to the right in orderto restore the craft to balance. Figure 22 illustrates the appearance ofthe instrument when the plane is in a diving or nose low position withits right wing low.

It will be observed from the above that the instrument is simple inconstruction and operation and positive in its reading; indicateslongitudinal and lateral unbalanceof the plane; indicates stresses towhich the plane is subjected, as when pulling out of a dive; affords amodulated action; has a very large surface contact between the liquidand the spherical chamber in proportion to the small volume of theliquid in the chamber; and serves fully the purposes of an artificialhorizon and of a stress or force indicator.

It wil1 be observed additionally that the sirnplicity of the instrumentmakes it comparatively inexpensive in cost. Still another important advantage is that the instrument'does not require any ancillaryattachment, in the nature of a Venturi tube or an air motor, as isnecessary with conventional gyroscopic types of instruments such asartificial horizons. I

It will be observed that the construction of the device, the functions,and results achieved thereby and the use of two liquids, one such asmercury being an electrical conductor, and the other such as oil beingdielectric, renders the device readily adaptable for connection withautomatic means for controlling the craft. Thus, by connecting theelectrical circuit of the controlling means to the instant device bymeans of contacts positioned adjacent the plane of separation of the twoliquids and at positions degrees displaced with respect to each otherany change in the position of the housing and contacts with respect tothe horizontal will cause certain of the contacts projecting into theliquid containing chamber to be engaged or contacted by a liquiddifi'erent from the liquid that normally contacts the same when thedevice is at a level flight position and will hence control the circuitsto the automatic flight position control means.

It will be apparent that the contacts may be arranged either in closedcircuit relation engaged by the mercury with the circuit to be openedupon variation in the liquid level, or may be of the open circuit typewith the circuit to be closed upon engagement of the contacts and themercury when the instrument is tilted.

I claim:

1. An aircraft instrument comprising a housing having a sphericalchamber defined in part by a transparent member, said housing having anelongated rearwardly radially extending horizontal passage communicatingwith said chamber and a vertical passage whose upper end communicateswith said first passage, a buoyant sphere in said chamber said spherehaving a radius slightly smaller than said chamber, an elongated armconnected to said sphere and extending through said horizontal passage,means pivotally mounting the rear end of said arm in said passage, aWeight shiftable in said vertical passage, a spring normallycounterbalancing' said weight, extensible means connecting said weightand an intermediate portion of said arm, two

liquids of difierent specific gravities and contrasting colors fillingthe space in said chamber around said sphere, and a flexible sealingmember adjacent the mouth of said horizontal passage.

2. An aircraft instrument comprising a housing having a sphericalchamber defined in part by a transparent member, said housing having anelongated horizontal passage branching from said chamber and adownwardly extending pas-, sage branching from said horizontal passage,a buoyant sphere in said chamber, said sphere being smaller than saidchamber, a rigid rod mounting said sphere at one end and extendingthrough and pivotally mounted in said horizontal passage at its oppositeend, a weight shiftable in said vertical passage, a spring normallycounterbalancing said weight, means suspending said weight from anintermediate portion of said rod, a flexible sealing member spanning theinner end of said horizontal passage and having a sealed connection withsaid rod, and two liquids of contrasting colors and different specificgravities filling the space in said chambers around said sphere.

3. An aircraft instrument as defined in claim 2, including a liquid insaid passages, and a chambered member communicating with and extendingupwardly from said horizontal passage and above the level of the liquidtherein.

4. An aircraft instrument as defined in claim 2, 'and marks on saidtransparent member adjacent to and above and below the plane ofseparation of said liquids when said instrument is in normal position,and each of said marks being of: h saint-v coi'br as h iiuifi di ili whb i ks are normal y. ii it s 'b e but becomegapparent against thebackground; of the liquid of contrasting color when the position ofthejinstrument variesfromnonnal. x H 5. An aircraft instrumentcompris'in g a hou sing having a chamber therein defined inpart byatransparent member, a buoyant mem; er shiftable in said chamber, aweightseparate from the buoyant member shiftable in said housing andconnectedwith said buoyant member toishift. sa m mb a r nen rme ly untrb lancine v' ld.. w i' t and twol ui s; f 1 trasting appearance anddifferent specific grav; ities filling the space in said chamber aroundsaid buoyant member. a u I u h t 6. An aircraft instrument as defined inclaim 5, andv inclicia on said transparent member and co-acting with theliquids of contrasting appear mice for measuring changes in the ievelofthe plane of separation of said liquids when said buoyant membershifts in said chamber. a

'7; An aircraft instrument comprising a housi'ng having a sphericalchamber therein; defined in part by a transparentmember, a small quan:tity of I a liquid of, one color Within said chigln l oer a sphere insaid chamber of a radiusslightly smaller than the radius qf said chamberand ad ted to fl atin s d liqui a jse i ui f .difier n a d v o mongravity than said first liquid substantially filling h e e s id. du b ai n and abqve id firs li u arid m i saidsphere for movnient to and fromn atior'i in said chamber incident to centrifugal -r e a i 8,.Anair'cra1f in trument defined in c '"'m 7, wherein th voll'inies ofsaidli ds are s o' proportioned that the plane of se'parationtherebtween cpincmesuwim the c'entr pla chamber when d Sphere is infnorl 1 -J P aircraft n tr ment a defin d i-cl im 7, wherein saidtransparent member is of substan tially semi;spheriucal conqcaveuoonyeig term;

ill. 'Anairfcraft inst ins t. e a mounted on "r pivdted tbsaid'fieiisirig, aim t liquids or difier it carers and different s"cific graviti es'subsftantially filliii: said enamarid immersing saidmernur saiu member ri 'i a y flaatizig'in 'said'liqiiids; ariaandrfiiany c uriterbalanced weig t shiftably cai'ri'ed 'by'saidhtiusi'ng and suspended from said arm;

11. An aircraft instrum'ent'comprising' ahous ing'iiaving achamb'ei-therin define'd in'part 'by a transparent member; "a; liquiddisplacement ninibershiftable within'saidchamberg and two li uids of"diflere'nt .icoidrs and different "specific era" ties substantiallyfilling said chamber and mmersing said member, said member normallfloating in said liquids, a normally counterbalanced weight shiftablycarried by said housing, and "extensible means suspending said Weightfrom said member.

12'. A level indicating instrument cbfl'iprislng'a housing, atransparent member "carried byfsaid housing and cooperating'therewith'to defin'ea chamber, two liquids of different "colors anddifferent specific gravities in said chamber, at least on marking onsaid member immediately below the normal plane of'separ'atiori bf saidliquids and of 'the same color as th'eheavy liquid;and at least onemarking on said member immediately concavefconvex ror'niand saidmarkings are 'e'lon gated and "extend iinplaries' parallel to the normalplane of liquid separation. I u q 15.4 i've indies mg; instriii'ent asdefih'd in claim 12, wherein said markings are elongated and extend inplanes parallel to the normal piane of liquid separation. v H o I 4 a s.Ari aircraft inst ument imprising an ing" having a chamber conta 'ng aquantity of liquid, 9, displaoe 'nent member r' 'cluding a ba y'- antportion smai er man said e iam i a many fioatifiginsaid liquid, a weightv f 1d member and adapted to mov ls (1 e 'nfi maime aims. 've t s te aspring normally couiiterbaiamifig a liquid, a movable \vi'glit-a uatednsimme i litx ctineupen, sa aflrsb r i s tality to displace said liquidands aid center point." and means exerting a-substantial-ly constantforge on said last-named instrumentality to normally counterbalance thesame. v 20; An aircraft instrument comprising a mounting;a'sel-f-leveling instrumentaliity shift able in saicl mount-ing about acenterpoint by gravity including a liquid; meansexerting a cent u a V rble q pe P 1. sa lmtri meni liiy to dis 8.191. li d and said e er Pointin said mounting, and means exerting a substah el ,consian norma ly.e eforce pn's id firs 31 In net. K

21A e' elrinsllp t ns i ruifieht qmfii a si M n r'ai meinb r'e' i d F 11said h s g a q o r ins.,-.theiiew F9 chamber; two liguidsof differentcolors aria ferent speci-flo-gravities in said chamber a plu rality ofmarkings on said member adjacent and below the normalplane of separationof said liquids and of the same coloras said heavy liquid, andaplurality of markings on said members a djac'ent'and above the normalplaneof liquid separation and ofthe same color asthe lighte i liquid,saidmarkings'including two direction indicating markings of each color,parallel to the plane of liquid separation and at apposite sides of saidmember, the upper pair of markings pointing inwardly and the lower pairof markings pointing outwardly.

22. A level indicating instrument comprising a housing, a transparentmember carried by said housing, and cooperating therewith to define achamber, two liquids of different colors and difierent specificgravities in said chamber, a plurality of markings on said memberadjacent and below the normal plane of separation of said liquids and ofthe same color as said'heavy liquid, and a plurality of markings on saidmember ad- Jacent and above the normal plane of liquid separation and ofthe same color as the lighter liquid, said markings including an upperupwardlypointing direction indicia and a lower downwardly-pointingdirection indicia.

23. A level indicating instrument comprising a chambered housing havinga transparent chamher-defining portion, two liquids of different colorsand different specific gravities in said housing chamber, a pair ofspaced inwardly pointing markings on opposite side of said transparentportion parallel to and above the normal plane of liquid separation andof the same color as said lighter liquid, and a pair of spaced outwardlypointing markings on opposite sides of said transparent portion parallelto and below the normal plane of liquid separation and of the same coloras said heavy liquid,

24. A level indicating instrument comprising a chambered housing havinga transparent chamher-defining portion, two liquids of different colorsand diiierent specific gravities in said housing chamber, a plurality ofdirection-indicating markings of the same color as said light liquidarranged on said transparent portion in laterally spaced relationadjacent and above the normal plane of separation of said liquids, and aplurality of direction-indicating markings of the same color as saidheavy liquid arranged on said transparent portion in laterally spacedrelation adjacent and below the normal plane of separation of saidliquids.

25. A level indicating instrument comprising a chambered housing havinga transparent chamber-deflning portion, a float in said chamber,centrifugally responsive means for shifting said float in said chamber,two liquids of difierent colors Within the chamber, a movable weightedelement which is normally counterbalanced and which is responsive to theapplication of centrifugal force thereto, whereby the movement of theelement is in proportion to the amount of force applied, and means forconnecting the element to the displacement member so that the movementof the element is transmitted to the member, whereby the movement orsaid member and the resultant change in the level of the liquid withinthe chamber is proportional to the force applied to said weightedelement.

ARTHUR Z. BENDAR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,376,727 Pentz May 3, 19211,409,537 Franzler Mar. 14, 1922 1,806,971 Greenhouse Mar. 26, 19311,948,612 Bouchard Feb. 27, 1934 1,957,897 Micek May 8, 1934 2,093,241Hegenberger Nov. 9, 1937 2,153,565 Isaacson Apr. 11, 1939 2,207,950Steensen July 16, 1940 2,296,750 Tucker Sept. 22, 1942 FOREIGN PATENTSNumber Country Date 110,565 Great Britain Oct. 25, 1917 152,488 GreatBritain Sept. 10, 1919 449,985 France Jan. 7, 1913 465,373 France Apr.15, 1913 263,414 Germany Aug. 8, 1913

